This invention relates to silver catalysts and their use in olefin epoxidation. More particularly, it relates to silver catalysts containing low levels of magnesium promoter.
Epoxides are reaction intermediates useful in production of numerous polymers, solvents and resins.
Direct oxidation of olefins with air or with gases containing molecular oxygen can be carried out by contacting the olefin vapor with the molecular oxygen in the presence of a silver-containing catalyst. The reaction is generally performed under conditions such that the olefin is in the vapor state. Part of the olefin is disadvantageously oxidized into carbon dioxide and water. It is desirable that the reaction be as selective as possible to the epoxide. A second consideration is the reactivity of the catalyst. The reactivity should be sufficient to allow an acceptable rate of production. Thus, an important feature of a catalyst is a good combination of selectivity and reactivity under reaction conditions. Generally, catalysts are supported to increase their performance and effective surface area.
It is known to use a supported silver catalyst with co-promoters, one of which is taught may be magnesium at 0.1 to 50 atomic percent based on silver. See U.S. Pat. No. 4,007,135.
U.S. Pat. 4,242,235 teaches that ethylene epoxidation can be catalyzed with a supported silver catalyst containing 0 to 2 weight percent (based on total catalyst weight) magnesium promoter.
U.S. Pat. No. 4,400,308 teaches use of a supported silver catalyst containing 0.05 to 0.5 weight percent (based on total catalyst weight) alkaline earth promoter to convert alkenes to epoxides.
While known catalysts are sufficient to effectively oxidize ethylene to ethylene oxide, they generally have a low selectivity when epoxidation of propylene is attempted. It is desirable to have a catalyst having better selectivity and activity for the epoxidation of propylene to propylene oxide.